Because you can come up with an infinite number of values but if you have a finite amount of space and certainly a computer has a finite amount of disk space or RAM, you have to make approximations.

你可能会碰到一些无限的值,如果你只有有限的空间,废话，电脑当然只有一个有限的磁盘空间,或RAM，我们得做一些近似处理。

哈佛公开课 - 计算机科学课程节选